Wheel balancing?

Everything about building wheels, glueing tubs, etc.
TimF
Posts: 108
Joined: Wed May 09, 2012 11:18 pm

by TimF

Spotted this online, first I've heard of it. How many of you are familiar with this / actually do it? Does it make much difference?

https://www.youtube.com/watch?v=UpSrrVV0XNE

Cheers...

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kdawg
Posts: 125
Joined: Wed Nov 20, 2013 9:10 pm

by kdawg

I like his videos (changed my chain cleaning regime recently because of him...) and that looks interesting.

The Park Tool guys disagree - although their main criticism seems to be for tubeless MTB.

https://youtu.be/CZMhdmtYDtw

If anyone has stories of it improving their wheels I’d be tempted to have a go though as it makes a bit of sense. I definitely get a slight undulation with the bike in a stand - but I’m not sure if that matters in the real world.
I'm left handed, if that matters.

by Weenie


mattr
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Location: The Grim North.

by mattr


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pdlpsher1
Posts: 2424
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

Yup. I do it for all of my wheels. None are terribly out of balance but some are worse than others. I bought some lead weights off of eBay. They seem to make a positive difference on the bike stand so I'm sure there's a difference on the road although I can't feel the difference.

alcatraz
Posts: 2202
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

It's possible to quantify imbalance. Small is ok, big is bad.

The more revs a wheel has the worse a problem it is. So at higher speeds or smaller wheels, the same imbalance would be more likely felt.

Seems the language about the problem is only yes/no which is odd. :)

A 5gr imbalance on 700c at 90km/h can be a problem.

A 15gr imbalance on a 700c at 30km/h no problem.

A 10gr imbalance on a 26inch going downhill at 45km/h could be a problem.

Besides, it's somewhat of a subjective issue. Do it if you like. Chances are you won't need it but if you have time and care about balance then it's quite nice.

I found it interesting that the parktool guys didn't try to match up the tire(or tube) imbalance opposite to the wheel's to eliminate some balance weights. Maybe it's too small to measure.

Hexsense
Posts: 933
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

I only partially done it.
Only counter weight opposite of valve to lessen the imbalance. But not completely remove the imbalance or even overcompensate it.
Totally perfect is hard. Make vibration non significant is easy.

snaxez
Posts: 36
Joined: Fri Jun 06, 2014 7:14 pm
Location: Estonia

by snaxez

I was thinking about the silca SpeedBalance, but not sure if it`s worth it. Campagnolo Bora has already added more weight on the other side if the valve hole.

youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

Wheel balance is critical for performance. Anyone riding unbalanced wheels—especially those in the Pacific Northwest who compete in my age group—is throwing watts away unless they add at least 500 grams to each rim in order to maintain this critical balance. Also, non-aero rims are MUCH easier to balance, as are tubular rims with TUFO tires attached by tape.

Ugh. No, wheel balance on road bikes doesn’t matter. People are attracted to the idea by analogy with car wheels and also because human beings love the idea of keeping things “in balance”. Don’t let a shaking workstand confuse you...it’s meaningless because it lacks the rider’s weight, and also the workstand acts as a soft spring. You can see a resonance in the bike/stand system, but othe road—with the rider’s weight and without the workstand—resonances are completely different.

The guy in the OP’s video seems to say, “hey, we can balance wheels! And clearly, the fact that we can balance them means we should balance them. There must be some benefit or we wouldn’t be able to do this.” In other words, there’s no real benefit articulated, at least not that I saw.

In all seriousness, balancing wheels doesn’t hurt anything except that it makes your bike heavier and therefore slower up hills. Do it if it makes your OCD soul happy, but don’t expect any benefits beyond that.

mattr
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Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

+1 unless the wheel and tyre are actually faulty and have a massive imbalance (faulty layup, bad extrusion, shit tyres), there is a vanishingly small effect, even when you get to triple digit speeds.

Butcher
Shop Owner
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by Butcher

https://www.omnicalculator.com/physics/ ... ugal-force

I entered 9 grams in this calculator and found it would cause the wheel to be out of balance around 1.2 lbs at 30mph and 3.2 lbs at 50mph.

When you have nothing else to do and have the best components, why not spend a bit of time to have them work in harmony.

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Lelandjt
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Joined: Tue Jan 19, 2016 7:10 am

by Lelandjt

I haven't added weights but I do avoid long valve stems for this reason.

ichobi
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Joined: Thu Jan 19, 2012 11:30 pm

by ichobi

I do it purely for the satisfaction of the fact that i can rev my wheel up and it doesnt shake off balance whatsoever. Makes me grin every time.

youngs_modulus
Posts: 575
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Location: Portland, OR USA

by youngs_modulus

Butcher wrote:
Mon Mar 18, 2019 3:56 pm
https://www.omnicalculator.com/physics/ ... ugal-force

I entered 9 grams in this calculator and found it would cause the wheel to be out of balance around 1.2 lbs at 30mph and 3.2 lbs at 50mph.
Those numbers check out. But consider this: for a 150 lb - 250 lb bike/rider system, 3.2 lbs is 2.1% to 1.3% of the system weight--that's not much, relatively speaking. This is why the vibration that's so obvious on the workstand is almost always imperceptible on the road. In contrast, sprinting at 35 mph means you're generating 5-6 lbs of thrust at the rear tire contact patch on average. But the actual thrust varies (roughly) sinusoidally between 0 and maybe 10 lbs of thrust depending on where you are in the pedal stroke. A 3-lb oscillation doesn't mean much when projected onto a 10-lb oscillation. I mean, it's not nothing, but we don't see Cavendish's rear wheel (or the rear wheel of other pro sprinters) skipping around because it hasn't been properly balanced.
Butcher wrote:
Mon Mar 18, 2019 3:56 pm
When you have nothing else to do and have the best components, why not spend a bit of time to have them work in harmony.
Why not? Because your wheels are already working in harmony--they're both round. Plus, adding weight is counter to the ethos of Weight Weenies. ;)

More seriously, "working in harmony" sounds like a really desirable thing, but the phrase doesn't have much meaning in this context. I'm not criticizing you, Butcher, but rather the sloppy thinking that often surrounds this issue. One often hears this language as part of an appeal to intuition and "rightness" rather than science. I suspect many people have experienced an out-of-balance front wheel on their car and felt the resulting steering wheel vibration. When the out-of-balance wheel is balanced, the vibration goes away, which feels much better. The thing is, a car wheel is a lot like a bike in a workstand because it's attached to the car with a soft spring. (The workstand's soft spring is the main vertical shaft).

Josh Poertner at Silca is definitely a smart guy and I respect his work. But he calls the spike in rolling resistance on rough surfaces at high pressure "impedance losses." IMHO, this is an understandable-but-suboptimal metaphor for what's going on, but I also sense some cognitive dissonance here. Silca sells wheel-balancing weights, but in nearly every real-world case, unbalanced wheels are imperceptible by the rider. This is a high-impedance system because the forcing frequency results in almost no relative motion. In other words, the impedance is high but the losses are negligible. I respectfully disagree with the term "impedance losses" for rolling resistance, but if Poertner likes that term, he should refrain from making his claim of "improved handling" due to wheel weights, because the mechanical impedance between the bike/rider system and the unbalanced wheel is so high that a balanced wheel isn't perceptibly different.

The paragraph above isn't there to call out Poertner or his collaborator Tom Anhalt; IMHO they both do solid work, Anhalt especially. This is just (IMHO) an easily-overlooked point of cognitive dissonance. Plus, wheel weights have a whiff of snake oil about them. On the other hand, people eagerly buy these things and Poertner has to keep the lights on* at Silca, so I'm not unsympathetic.

I agree that balancing wheels gratifies some people immensely and does no harm, so IMHO your advice is totally sound. One interesting experiment would be to attach a weight near the valve stem to exaggerate the imbalance and see if you can tell the difference. Ideally, you'd have a friend attach the weight to either eliminate the imbalance or accentuate it; if the rider can reliably call the wheels balanced or unbalanced, then it's likely their perceptions are worth something. If you do 10 runs and the rider correctly calls the weight position 6 times out of ten, you need to do more runs. If you did 100 runs and the rider deduced the weight position correctly 67-90% of the time (roughly speaking) then the perception is likely real.

Another thing: lots of valve stems on high-end tubes are made of brass. Silca's Vittoria-sourced latex tubes use aluminum valve stems, as may some other brands. If your wheel is heavy at the valve, doesn't it make more sense to use a lighter valve than to add weight opposite the valve? And if you're going to add weight to the valve, why not get a more robust brass stem to start with rather than adding weight next to an aluminum valve?

The upshot is that it's fine to balance your wheels if that makes you happy. It just won't make you any faster or make your bike handle any better.


* Margins in the bike industry suck, possibly even for $36 wheel weights. Virtually no one gets rich from bikes, and those that do get rich very slowly (e.g., Mike Sinyard and the Burke family, which owns Trek). The idea that bike-industry titans are manipulating the bike market so they can swim in vaults full of gold coins like Scrooge McDuck is laughable to anyone who has spent substantial time in the industry.

youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

ichobi wrote:
Mon Mar 18, 2019 8:26 pm
I do it purely for the satisfaction of the fact that i can rev my wheel up and it doesnt shake off balance whatsoever. Makes me grin every time.
Yeah...this is totally legit. I'm being completely earnest here. If it makes you happy, knock your socks off.

youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

I didn't address speed wobble in my earlier post. Due to the analogy with car wheels, some people may think that speed wobble is a resonant phenomenon. It isn't. I admit I assumed that it was until I read this letter to Velonews' Lennard Zinn.

It's not resonance; it's a Hopf bifurcation, which is more like the flutter your rain jacket develops above certain speeds. The difference is subtle and hard to explain without getting hopelessly technical. Here's a concrete example of a Hopf bifurcation: speaking. The vibration of your vocal chords isn't due to resonance...it starts because of a Hopf bifurcation. That's why you don't have to alter your breath rhythmically (creating a forcing frequency) in order to speak. As long as air is flowing over your vocal chords at a sufficient velocity, they'll vibrate. Bikes and rain jackets are like that too--they don't require a forcing frequency in order to flutter/wobble.

Perfectly balanced wheels would provide no forcing frequency, and wobble would happen anyway. So no, speed wobble isn't a result of unbalanced wheels. That said, grossly unbalanced wheels might allow a Hopf bifurcation to occur at a lower speed than it otherwise would. When I was a junior, I borrowed a disc wheel for the district TT championship. At about 38 MPH and with the disc installed, my Ciöcc would wobble violently. With my regular rear wheel installed, it wouldn't. Unbalanced wheels don't cause speed wobble due to a forcing frequency, but it may be that the onset of bifurcation happens at a lower speed with an unbalanced wheel than it does with a balanced wheel. This is similar to a rain jacket made from a stiffer material fluttering at higher speeds than a jacket made of a more supple material.

I admit that sounds a lot like "unbalanced wheels can cause speed wobble," but it's not quite the same. Maybe Poertner was thinking of Hopf bifurcations when he mentioned "improved handling" in his ad copy for wheel weights. Fair enough. But the vagueness of "improved handling" seems (at least to me) contrary to the spirit of the substantial work that Poertner has done in making rolling resistance and drag data available to consumers in general.

by Weenie


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